Damper blade and damper blade assembly for an air duct

ABSTRACT

A damper plate assembly adapted for installation in a circular air duct having tubular walls defining a bore about a central air flow axis with a set of coaxial apertures in opposing walls, the damper plate assembly including:
         a. a disk-like damper plate having (i) a central body part with a peripheral edge region, and a set of first and second holes extending transversely through the damper plate and situated along a diametrical line 180 degrees apart in first and second opposite portions respectively of the peripheral edge region, and (ii) a finger-like projection extending in the plane of the disk radially outward of the first peripheral edge region along the diametrical line, and   b. first and second pivot elements adapted to engage the first and second opposite peripheral portions, the first pivot element having a body part with proximal and distal ends along a central longitudinal axis and extending axially from the distal end a set of two fingers which have a closed unflexed state where the fingers are generally closely parallel, the fingers being resiliently bendable apart from each other to a flexed state and biased to return to their closed state, one of the fingers including a projection extending transversely of the central longitudinal axis toward the other finger, and the other finger having a recess into which the projection extends when the fingers are in their closed state.

I. BACKGROUND

A. Field of the Invention

This invention relates to a mounting assembly for installation and adjustment of a pivotal damper blade within an air duct system.

B. Description of Related Art

Conventional heating, ventilating and air-conditioning (HVAC) systems utilize vast lengths of sheet metal duct work to convey conditioned air throughout buildings of all types, including residential, industrial, office, medical and apartment buildings. Such HVAC systems include a great many pivotable damper blades situated in air ducts at selected locations to facilitate adjustments at the air flow as required. Installation of all these dampers and subsequent adjustment by installers or service personnel to “balance” the air duct systems is typically a substantially time-consuming process.

In many conventional circular tube HVAC duct systems each damper is a circular disk pivotably mounted via bearing elements mounted on the side and extending through a set of aligned holes cut in opposite facing side walls of duct segments. Typically two bearing elements are mounted on opposite peripheral edge regions of the disk, one being a fixed pin extending radially outward, and the other being a spring-biased pin, also extending radially outward 180° apart from the fixed pin. These pivot elements allow the damper blade to pivot from a closed position in which it substantially blocks the air flow to an angled position in which it permits different degrees of airflow.

In some prior art assemblies there is a first finger-like projection extending from one peripheral edge of the damper blade for insertion into one aperture in the duct side wall, and a second pivot element spring-mounted on the opposite edge of the damper blade for extension outward through a hole in the duct wall coaxial with the first hole. Finally, there is a handle or lever attached or extending from said second pivot element for allowing a service person to manually pivot and fix the pivoted position of the damper blade within the duct. Typically, this arrangement includes a collar element and set screw associated with said second pivot element for adjustably fixing the damper blade or its turning handle in selected pivoted position pursuant to the desired airflow.

Also, in conventional HVAC duct systems the turning handle stands off about two inches externally of the sheet metal to permit wrapping of installation on external surfaces of the duct, while still permitting access to the damper blade for adjustment of the airflow. Another common feature is a seal element to reduce or prevent leakage of outside air to flow into the duct or of inside air to flow outward of the duct along the side of the pivot elements where they extend through a hole in the duct wall.

Examples of a few prior art duct systems and components are disclosed in the following patents. U.S. Pat. No. 4,715,581 discloses an assembly of a damper blade pivotally mounted within a duct by a first pivot pin extending from one side of the blade and a second pivot pin extending through the duct wall into a clip mounted on the blade, the second pin being spring-biased to an extended position and having a retracted position for installation.

U.S. Pat. No. 6,209,850 discloses a damper blade mount assembly using two spring clamps secured to opposite peripheral edge areas of the blade and pivot pins introduced through opposite coaxial apertures in the duct walls to engage the clips.

U.S. Pat. No. 2,285,829 discloses a damper blade with clips and pivot pins secured to opposite peripheral areas of the blade to extend through coaxial apertures in the duct walls. Each clip is an elongated strip folded in half with tabs of one-half extending through the blade into mating holes in the other half of the strip.

U.S. Pat. No. 5,921,277 discloses an assembly of a damper blade as a paddle mounted only at one end of a pivot rod extending through a single aperture in a wall of the duct.

II. OBJECTS AND SUMMARY OF THE INVENTION

Prior art assembles of the type described above have numerous component parts and require substantial time for installation and subsequent adjustment or balancing.

The present invention seeks to significantly reduce the number of components required in a damper blade assembly and to reduce cost of manufacture by more efficient use of material to produce the parts, and to significantly reduce time spent in assembling and installing these parts and adjusting the installed damper blade when balancing the system.

One specific object of the present invention is to employ an extremely simple damper blade which is essentially a flat plate with two small apertures in the surface and without clips or spring biased elements as parts of the blade.

A further object is to achieve installation of the damper blade merely by inserting two pivot elements inward through opposite holes in duct walls to engage peripheral edge regions of the damper plate.

Another object is for at least one of these pivot elements to have outward projections on its external surface for engagement with the edges of the aperture in the duct wall through which it is inserted inwardly, these projections to restrain the pivot element from being moved or pulled axially out of the hole in the duct wall. In a preferred embodiment these projections would be external threads of a standard pitch to later receive and cooperate with a wing nut or equivalent, which when screwed onto said external threads, locks against the duct wall and fixes the axial position and rotational orientation of the pivot element.

A still further object is for the pivot elements each to be a simple one-piece, preferably molded device having at one end a pair of resilient but strong axially-extending and slightly spaced apart fingers that can, after insertion inwardly through the hole in the duct wall, engage and capture between them a peripheral edge portion of the damper plate. An axial segment of the outer surface of each pivot element serves as a bearing for the pivoting of the damper plate within the duct.

In a further preferred embodiment one of the adjacent and parallel fingers of the pair of fingers includes a projection extending transversely or perpendicularly from said finger toward a recess or cooperating part of the other finger. At the time of attachment of the set of fingers to the peripheral edge region of the damper plate, the distal ends of the finger slide over and sandwich between them an area of the peripheral edge region of the damper plate, and said transverse projection of one finger snaps through an aperture in the peripheral edge region of the damper plate and thence into the cooperating recess of the other finger. This avoids placing clips and/or other spring loaded hardware on the damper blade, and instead provides means on the plate to receive the pivotal hardware elements from outside of the duct. Thus, installation is simplified to requiring only a set of two coaxial holes in opposite sidewalls of the duct, and two pivot and securing elements inserted from the outside through said holes to engage adjacent peripheral edges of the damper plate.

One of the two pivot elements extends substantially further outward of the aperture in the duct wall and then extends transversely of the axis of the pivot element, as a handle or lever. When the HVAC system is balanced such handle or lever is turned to pivot the damper plate between its closed position where the plane of the plate is perpendicular to the air flow axis of the duct, and a 90° pivot therefrom putting the plane of the plate parallel to the flow axis to allow maximum airflow, or to any angular position therebetween. The selected angular position of the plate is later maintained by a wing nut pivotally engaged to the pivot pin which includes the handle. Thus, an operator or technician who rotates the wing nut to an open position can with his other hand easily engage the closely adjacent lever, rotate or pivot the damper plate, and re-tighten the wing nut.

The present invention includes: the new damper plate and externally inserted pivot elements as:

(a) a set of damper plate and pivot elements assembled together or in unassembled kit form,

(b) the new damper plate alone,

(c) the new pivot elements alone, and

(d) the combination of an assembled HVAC duct segment and new damper plate and pivot elements.

Descriptions of preferred embodiments of selected ones of the above embodiments are as follows.

1. A damper plate assembly adapted for installation in a circular air duct having tubular walls defining a bore about a central air flow axis with a set of coaxial apertures in opposing walls, comprising:

a. a disk-like damper plate having (i) a central body part with a peripheral edge region, and a set of first and second holes extending transversely through said damper plate and situated along a diametrical line 180 degrees apart in first and second opposite portions respectively of said peripheral edge region, and (ii) a finger-like projection extending in the plane of said disk radially outward of said first peripheral edge region along said diametrical line, and

b. first and second pivot elements adapted to engage said first and second opposite peripheral portions, said first pivot element comprising a body part with proximal and distal ends along a central longitudinal axis and extending axially from said distal end a set of two fingers which have a closed unflexed state where said fingers are generally closely parallel, said fingers being resiliently bendable apart from each other to a flexed state and biased to return to their closed state, one of said fingers including a projection extending transversely of said central longitudinal axis toward the other finger, and the other finger having a recess into which said projection extends when said fingers are in their closed state, said first pivot element adapted to have its fingers inserted inwardly through one of said apertures in said duct wall to engage and sandwich between them said first portion of said peripheral edge of said plate with said projection of one finger inserted through said first hole in said plate's peripheral edge region and into said recess of said other finger for locking engagement of said pivot element with said damper plate,

c. said second pivot element having a similar body part and set of fingers as said first pivot element for being similarly insertable inwardly through said second of said apertures in said duct wall, for engaging said second peripheral edge region of said plate and said second hole through said plate,

d. said second pivot element further comprising on its body part at least one wall-engaging projection extending transversely of its central longitudinal axis and adapted to engage edges of said duct wall in the vicinity of said aperture in said duct wall to restrain said body part from moving axially outward of said aperture after said second pivot element has been inserted into said aperture, and

e. a fastening element adapted to cooperate with said body part of said second pivot element for securing said second pivot element and damper plate coupled thereto by said set of fingers of said second pivot element in a selected rotatable position about its central longitudinal axis relative to said duct wall.

2. A damper plate adapted for installation in a circular air duct having tubular walls about a central air flow axis, comprising:

-   -   a disk-like central body part with a peripheral edge region and         a set of two holes extending transversely through said plate and         situated along a diametrical line 180 degrees apart in first and         second opposite portions of said peripheral edge region, and a         finger-like projection extending in the plane of said disk         radially outward of said peripheral edge region along said         diametrical line.

3. A pivot element for a disk-like damper plate used in an air duct damper assembly, where said damper plate has a central body part with a peripheral edge region and a set of first and second holes extending transversely through said plate and situated along a diametrical line 180 degrees apart in first and second opposite peripheral edge portions respectively,

said pivot element adapted to engage one of said peripheral edge portions, said pivot element comprising a body part with proximal and distal ends along a central longitudinal axis, and extending axially from said distal end a set of two fingers which have a closed unflexed state where said fingers are generally closely parallel, said fingers being resiliently bendable apart from each other to a flexed state and biased to return to their closed state and biased to return to their closed state, one of said fingers including a projection extending transversely of said central longitudinal axis toward the other finger, and the other finger having a recess into which said projection extends when said fingers are in their closed state, for locking engagement of said pivot element with said damper plate.

These and other objects of the present invention will become apparent as this description proceeds in conjunction with the following specification and appended claims.

III. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of the new damper and air duct assembly,

FIG. 2 is a top plan view taken along line 2-2 in FIG. 1,

FIG. 3 is a fragmentary side elevation view partially in section showing initial steps of assembling the damper blade in the housing,

FIG. 4 is a fragmentary enlarged side elevation view showing the right side peripheral edge region of the damper blade engaged by a finger of a pivot element,

FIG. 5 is a fragmentary enlarged side elevation view partially in section of the opposite pivot element whose distal end fingers engage the damper plate and whose proximal end includes a turning lever,

FIG. 6 is a top perspective view of the seal-washer component,

FIG. 7 is a top perspective view of the new damper plate alone, and

FIG. 8 is a top plan view of a sheet from which a plurality of new damper plates is punched.

IV. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-3 illustrate the new damper assembly 10 in a conventional HVAC duct system represented by duct segment 12.

A. The Damper Plate

The new damper plate 14 as seen in FIGS. 1-3 and 7 is as a disk-like element of diameter dimensioned to fit with appropriate clearance in bore 15 of duct 12. Plate 14 has a central part and a peripheral edge region and includes two apertures 16A, 16B in said peripheral edge region which are aligned along a diameter and pivot axis Y-Y. Adjacent to aperture 16A in plate 14 is a finger-like projection 18 which serves as a guide pin to enter aperture 20 (see FIGS. 3 and 4) in the wall of duct 12 during initial installation of plate 14. Within the scope of this invention it is also possible to utilize a rectangular or other shaped damper plate in duct of corresponding shape bore.

B. Installation of the Damper Plate

Installation is shown in FIG. 3 where plate 14 may be held vertically as shown by a solid line circle 14A or angled as shown by line 14B as it is lowered or otherwise positioned into duct 12 until its finger 18 enters aperture 20 in the duct wall. Then, first pivot element 24 is inserted inwardly through said aperture 20 where it engages the peripheral edge and aperture 16A of plate 14, the specific nature of this engagement to be described later. FIG. 3 also shows damper plate 14, represented by line 14C, as fully installed with second pivot element 26. Here, plate 14 is shown perpendicular to air flow axis X-X (seen in FIGS. 1 and 3). Finger 18 is preferably about ⅛-¼″ wide and about ½ to 1″ long, but dimensions may vary for different size ducts and damper plates.

C. Engagement of Damper Plate with Distal Pivot Element

For convenience herein, the pivot elements will be designated first or distal pivot element 24, being the one most distant from the operator when balancing the system, and second or proximal pivot element 26 being the manipulated by the operator.

FIG. 4 is an enlarged view showing the distal pivot element 24 having base part 30, a central shank part 31 with outside diameter dimensioned to fit with slight clearance through aperture 20 in the duct wall 12, allowing shank part 31 to rotate when damper plate 14 is pivoted during balancing of the system.

After pivot element 24 is inserted inward through aperture 20, its set of flexible and resilient fingers 33, 34 engage peripheral edge region 14F of plate 14 (see FIG. 4) and resiliently diverge slightly to allow edge region 14F to slide between them until projection 35 on finger 33 snaps through hole 16A in plate 14, and thence into recess 36 in finger 34. This engagement of pivot element 24 with plate 14 supports plate 14 for subsequent pivotal movement within duct segment 12.

Variations of fingers 33, 34 and their projection 35 into recess 36 are possible, such as short projections from both fingers extending into the hole 16A in the damper plate, or a projection from only one of said fingers, or a recess area in a surface of the damper plate for receiving the finger itself, or a still different elongated component that is insertable through an aperture in the duct wall and can easily and securely engage the edge of the damper plate.

D. Engagement of Damper Plate with Proximal Pivot Element (with Handle)

Attachment of the proximal pivot element 26 at the opposite peripheral edge region 14P of plate 14 (see FIGS. 4 and 7) with distal pivot element 24 is achieved as seen in enlarged FIG. 5. In a manner similar to attachment of distal pivot element 20, pivot element 24 has a set of resilient fingers 33A, 34A, projection 35A extending through aperture 16B in plate 14, and thence cooperating with recess 36A. A shank portion 40 has external threads 42 and handle or lever part 44. This handle may be integral with shank portion 40 or attached thereto. In one preferred embodiment the entire proximal pivot element is a one-piece molded component of a strong and resilient plastic such as nylon or other suitable plastic selected from many plastics well known in the prior art.

E. Wing Nut and Washer-Seal on Proximal Pivot Element

As seen in FIG. 5, wing nut 50 is engaged to pivot element 26 by threads 42 on the shank portion 40 of pivot element 26. Between wing nut 50 and the convex outer surface of duct 12 at the area of aperture 27 is washer-seal 52 having a flat side 53 adjacent wing nut and concave side 54 adjacent and conforming to the outer surface of duct 12.

F. Assembly and Balancing of Duct System

Before pivot element 26 is inserted into aperture 27, wing nut 50 and washer-seal 52 are positioned onto pivot element 26 in the axial area seen in FIG. 5. After that, pivot element 26 is inserted through aperture 27 and manipulated to engage peripheral region 15P of plate 14 with its fingers 33A, 34A securely engaging plate 14, and with projection 35A extending through aperture 16B of plate 14 and thence into recess 36A.

Next pivot element 26, via its pivot handle 44, is rotated, thus pivoting damper plate 14 to the desired angular position within duct 12, in the air flow balancing procedure. Finally, wing nut 50 is rotated until it and seal-washer 52 are snugly locked against duct wall 12, thus locking plate 14 in its angular orientation, until subsequently changed by reversing this procedure.

Threads 42 function as the obvious engagement means for wing nut 50, but also as projecting elements to engage the edge of aperture 27 which allows pivot element 26 to be inserted inwardly to a selected depth, and to restrain pivot element from being able to move axially outward. This restraint allows wing nut 50 to be tightened against washer 52 and against the wall of duct 12. Variations of the external threads 42 are possible such as a set of two closely adjacent circular ribs extending radially outward like said threads, or other intermittent projections instead of continuous circumferential threads or ribs.

Washer 52 allows wing nut 50 to seat properly and securely against wall 12, and also serves as a seal against air leakage into or out of duct 12 at the area of hole 27 where proximal pivot element 26 intersects the duct wall.

As compared to all known prior art, the new damper plate assembly as described, allows installation with a reduced number of components which are also substantially inexpensive to make, and allows installation in greatly reduced time and effort. Since the number of damper plate assemblies used throughout the country is in the hundreds of thousands, this improved assembly, if it becomes widely used, can have a very significant economic benefit. No set screw of prior art damper blade assemblies is required, because of the intimate and secure engagement of the fingers of the pivot elements with the damper plate. It is to be noted that the wing nut securement is required only on the proximal pivot element.

F. Manufacture of New Damper Plate and Pivot Elements

In the manufacture of components for this new assembly the damper plate is cut or pressed from a sheet of sheet metal. For maximum economy in use of material these damper plates 14 are cut, as shown in FIG. 8, where they are closely adjacent, and the integral guide finger 18 of each plate 14 is oriented along parallel axes Y-Y on the sheet to allow the maximum number of pieces per length of sheet material.

One complete assembly of this new arrangement comprises a single damper plate 14 with its own guide finger 18, distal pivot element 14 with its mating fingers, and proximal pivot element 26 and its mating fingers, (and separate or integral handle), washer-seal 52 and wing nut 50. This is an extremely simple, efficient and economic approach to manufacture and assembly for which there is need of hundreds of thousands of pivot assemblies.

While the preferred embodiment of the present invention has been shown and described above, it should be understood that within the scope of the appended claims, the invention may be practiced in other forms specifically shown herein. 

1. A damper plate assembly adapted for installation in a circular air duct having tubular walls defining a bore about a central air flow axis with a set of coaxial apertures in opposing walls, comprising: a. a disk-like damper plate having (i) a central body part with a peripheral edge region, and a set of first and second holes extending transversely through said damper plate and situated along a diametrical line 180 degrees apart in first and second opposite portions respectively of said peripheral edge region, and (ii) a finger-like projection extending in the plane of said disk radially outward of said first peripheral edge region along said diametrical line, and b. first and second pivot elements adapted to engage said first and second opposite peripheral portions, said first pivot element comprising a body part with proximal and distal ends along a central longitudinal axis and extending axially from said distal end a set of two fingers which have a closed unflexed state where said fingers are generally closely parallel, said fingers being resiliently bendable apart from each other to a flexed state and biased to return to their closed state, one of said fingers including a projection extending transversely of said central longitudinal axis toward the other finger, and the other finger having a recess into which said projection extends when said fingers are in their closed state, said first pivot element adapted to have its fingers inserted inwardly through one of said apertures in said duct wall to engage and sandwich between them said first portion of said peripheral edge of said plate with said projection of one finger inserted through said first hole in said plate's peripheral edge region and into said recess of said other finger for locking engagement of said pivot element with said damper plate, c. said second pivot element having a similar body part and set of fingers as said first pivot element for being similarly insertable inwardly through said second of said apertures in said duct wall, for engaging said second peripheral edge region of said plate and said second hole through said plate, d. said second pivot element further comprising on its body part at least one wall-engaging projection extending transversely of its central longitudinal axis and adapted to engage edges of said duct wall in the vicinity of said aperture in said duct wall to restrain said body part from moving axially outward of said aperture after said second pivot element has been inserted into said aperture, and e. a fastening element adapted to cooperate with said body part of said second pivot element for securing said second pivot element and damper plate coupled thereto by said set of fingers of said second pivot element in a selected rotatable position about its central longitudinal axis relative to said duct wall.
 2. A damper plate assembly according to claim 1 further comprising a turning handle extending generally perpendicularly and rigidly from said proximal end of said second pivot element.
 3. A damper plate assembly according to claim 1 further comprising a washer-seal element in the form of a cylinder having a bore through which is extendable said second pivot element, and one end surface perpendicular to the central axis of said cylinder, and an opposite end surface defining a concave shape conforming to the convex outer surface of the duct, said washer-seal element being positionable coaxially between said fastener and said duct wall outer surface.
 4. A damper plate assembly adapted for installation in an air duct having tubular walls defining a bore about a central air flow axis with a set of coaxial apertures in opposing walls, comprising: a. a damper plate having (i) a central body part with a peripheral edge region adapted to conform to and fit within said duct bore, and a set of first and second holes extending transversely through said damper plate and situated along a diametrical line 180 degrees apart in first and second opposite portions respectively of said peripheral edge region, and (ii) a finger-like projection extending in the plane of said damper plate radially outward of said first peripheral edge region along said diametrical line, and b. first and second pivot elements adapted to engage said first and second opposite peripheral edge portions respectively, said first pivot element comprising a body part with proximal and distal ends along a central longitudinal axis and extending axially from said distal end a set of two fingers which have a closed unflexed state where said fingers are generally closely parallel, said fingers being resiliently bendable apart from each other to a flexed state and biased to return to their closed state, one of said fingers including a projection extending transversely of said central longitudinal axis toward the other finger, and the other finger having a recess into which said projection extends when said fingers are in their closed state, said first pivot element adapted to have its fingers inserted inwardly through one of said apertures in said duct wall to engage and sandwich between them said first portion of said peripheral edge of said plate with said projection of one finger inserted through said first hole in said plate's peripheral edge region and into said recess of said other finger for locking engagement of said pivot element with said damper plate, c. said second pivot element having a similar body part and set of fingers as said first pivot element for being similarly insertable inwardly through said second of said apertures in said duct wall, for engaging said second peripheral edge region of said plate and said second hole through said plate, d. said second pivot element further comprising on its body part at least one wall-engaging projection extending transversely of its central longitudinal axis and adapted to engage edges of said duct wall in the vicinity of said aperture in said duct wall to restrain said body part from moving axially outward of said aperture after said second pivot element has been inserted into said aperture, and e. a fastening element adapted to cooperate with said body part of said second pivot element for securing said second pivot element and damper plate coupled thereto by said set of fingers of said second pivot element in a selected rotatable position about its central longitudinal axis relative to said duct wall.
 5. A damper plate adapted for installation in a circular air duct having tubular walls about a central air flow axis, comprising: a disk-like central body part with a peripheral edge region and a set of two holes extending transversely through said plate and situated along a diametrical line 180 degrees apart in first and second opposite portions of said peripheral edge region, and a finger-like projection extending in the plane of said disk radially outward of said peripheral edge region along said diametrical line.
 6. A damper plate according to claim 5 wherein said disk is a substantially flat sheet, and said finger-like projection is a contiguous part of said sheet
 7. A damper plate according to claim 5 wherein each of said holes is elongated in the direction of said diametrical line.
 8. A damper plate according to claim 5 wherein said finger-like projection has width in the range of about ⅛ to ¼ inch, and length in the range of about ½ to 1 inch.
 9. A pivot element for a disk-like damper plate used in an air duct damper assembly, where said damper plate has a central body part with a peripheral edge region and a set of first and second holes extending transversely through said plate and situated along a diametrical line 180 degrees apart in first and second opposite peripheral edge portions respectively, said pivot element adapted to engage one of said peripheral edge portions, said pivot element comprising a body part with proximal and distal ends along a central longitudinal axis, and extending axially from said distal end a set of two fingers which have a closed unflexed state where said fingers are generally closely parallel, said fingers being resiliently bendable apart from each other to a flexed state and biased to return to their closed state and biased to return to their closed state, one of said fingers including a projection extending transversely of said central longitudinal axis toward the other finger, and the other finger having a recess into which said projection extends when said fingers are in their closed state, for locking engagement of said pivot element with said damper plate.
 10. A combination air duct and damper plate assembly, comprising a. a length of a circular air duct having tubular walls defining a bore about a central air flow axis with a set of coaxial apertures in opposing walls, b. a disk-like damper plate having (i) a central body part with a peripheral edge region, and a set of first and second holes extending transversely through said damper plate and situated along a diametrical line 180 degrees apart in first and second opposite portions respectively of said peripheral edge region, and (ii) a finger-like projection extending in the plane of said disk radially outward of said first peripheral edge region along said diametrical line, and c. first and second pivot elements adapted to engage said first and second opposite peripheral portions, said first pivot element comprising a body part with proximal and distal ends along a central longitudinal axis and extending axially from said distal end a set of two fingers which have a closed unflexed state where said fingers are generally closely parallel, said fingers being resiliently bendable apart from each other to a flexed state and biased to return to their closed state, one of said fingers including a projection extending transversely of said central longitudinal axis toward the other finger, and the other finger having a recess into which said projection extends when said fingers are in their closed state, said first pivot element adapted to have its fingers inserted inwardly through one of said apertures in said duct wall to engage and sandwich between them said first portion of said peripheral edge of said plate with said projection of one finger inserted through said first hole in said plate's peripheral edge region and into said recess of said other finger for locking engagement of said pivot element with said damper plate, d. said second pivot element having a similar body part and set of fingers as said first pivot element for being similarly insertable inwardly through said second of said apertures in said duct wall, for engaging said second peripheral edge region of said plate and said second hole through said plate, e. said second pivot element further comprising on its body part at least one wall-engaging projection extending transversely of its central longitudinal axis and adapted to engage edges of said duct wall in the vicinity of said aperture in said duct wall to restrain said body part from moving axially outward of said aperture after said second pivot element has been inserted into said aperture, and f. a fastening element adapted to cooperate with said body part of said second pivot element for securing said second pivot element and damper plate coupled thereto by said set of fingers of said second pivot element in a selected rotatable position about its central longitudinal axis relative to said duct wall. 